1. Field of the Invention
The present invention is directed to the field of optical lenses, and in particular to a lens that produces a columnar focus with the axis of the focal column perpendicular to the principal plane of the lens.
2. Description of the Prior Art
The concept of utilizing a plasma generated by laser guided electric discharges in the atmosphere as the conducting element of an antenna was introduced by Vallese (U. S. Pat. No. 3,404,403) in 1968. By 1970 Vaill had succeeded in producing a laser guided streamer (J. R. Vaill, D. A. Tidman, T. D. Wilkerson, D. W. Koopman, "Propagation of High-voltage Streamers Along Laser-induced Ionization Trails," Appl. Phy. Ltrs., Vol. 17, No. 1, pp. 20-22, Jul. 1, 1970). The principal objective was the development of an antenna with no physical structure, but with large effective area. While the basic theoretical and experimental work for laser antennas has been successfully accomplished, the goal of producing an ionized column of atmosphere for use as an antenna, or to direct lightning strikes, has proved to be elusive. The main difficulty in the production of a viable plasma antenna lies in the tendency of the plasma initially created to block the radiation required to maintain the plasma in a columnar geometry. Various strategies have been used to overcome this difficulty. For example, Dwyer used a laser to weakly ionize an atmospheric column and then discharged a marx generator through the weakly ionized column to achieve a sufficiently high free electron concentration (T. J. Dwyer et al, "On the Feasibility of Using an Atmospheric Discharge Plasma as an RF Antenna," IEEE Trans. on Antennas and Propagation, Vol. APPLICATION-32, No. 2, pp. 141-146, February 1984).